Cancer continues to be a leading cause of mortality around the globe. Traditional regimens of cancer management have been successful in the management of a selective group of circulating and slow-growing solid cancers. However, many solid tumors are resistant to traditional approaches, and the prognosis in such cases is correspondingly grave.
One example is pancreatic cancer, the fifth leading cause of cancer-related deaths in the United States. It is associated with a high mortality rate, with the median survival for untreated patients estimated at approximately 4 months. Aggressive surgical intervention is an option for only about 10% of patients (those with Stage I disease), and extends median survival to ˜14.5 months.
The other 90% have locally advanced or metastatic disease, and are considered unresectable. Traditional therapy has only a modest effect on survival. The median survival of patients with Stage II, Stage III or Stage IV disease averages 4.5 months on a chemotherapy regimen of 5-fluorouracyl (5-FU) compared with 3.5 months without treatment (Frey et al., Cancer (1981) 47:27; Mallinson et al., Br. Med. J. (1980) 281:1590; Miller et al., Am. J. Roentgenol. Radium Ther. Nucl. Med. (1958) 80:787). Radiation therapy alone can reduce pain, but there is no significant improvement of survival (Gastrointestinal Tumor Study Group, Cancer (1985) 56:2563). The combination of chemotherapy with external beam radiation therapy has been employed, but there is no good evidence that such combination therapies are effective (Klaasen et al., J. Clin. Oncol. (1985) 3:373).
More recently, the chemotherapeutic agent, Gemcitabine (GEMZAR™) was shown to improve overall median survival to 5.7 months compared with 4.2 months for 5-FU, and had a better clinical benefit index. However, it is clear that even with these newer agents, palliation of the disease is highly temporary.
Another example is brain cancer. Each year, approximately 15,000 cases of high grade astrocytomas are diagnosed in the United States. The number is growing in both pediatric and adult populations. Standard treatments include cytoreductive surgery followed by radiation therapy or chemotherapy. There is no cure, and virtually all patients ultimately succumb to recurrent or progressive disease. The overall survival for grade IV astrocytomas (glioblastoma multiforme) is poor, with ˜50% of patients dying in the first year after diagnosis. Because these tumors are aggressive and highly resistant to standard treatments, new therapies are needed.
An emerging area of cancer treatment is immunotherapy. There are a number of immunological strategies under development. One example is the administration of biomodifiers such as cytokines, either systemically or into the tumor site. One pre-clinical study showed that interferon α-2a can augment the cytotoxicity of 5-FU. However, there was no clinical advantage of this over 5-FU alone (Bernhard et al., (1995) 71:102).
Another example is adoptive immunotherapy, using stimulated autologous cells of various kinds. One version is to stimulate autologous lymphocytes ex vivo with tumor-associated antigen to make them tumor-specific (Zarling et al. (1978) Nature 274:269; U.S. Pat. No. 5,192,537). Autologous lymphocytes and killer cells may also be stimulated non-specifically; for example, by culturing with a combination of IL-2 and IFN-γ (U.S. Pat. No. 5,308,626). Peripheral blood-derived lymphocytes cultured in IL-2 form lymphokine-activated killer (LAK) cells, which are cytolytic towards a wide range of neoplastic cells (Merchant et al. J. Neuro-Oncol. 8:173. A further possibility is the use of tumor-infiltrating lymphocytes (TIL), obtained by collecting lymphocytes infiltrating into tumors, and culturing them with IL-2 (Rosenberg et al. (1990) New Engl. J. Med. 323:570). Unfortunately, TILs can only be prepared in sufficient quantity to be clinically relevant in a limited number of tumor types, and remain experimental.
Another form of immunotherapy is the generation of an active systemic tumor-specific immune response of host origin by administering a vaccine composition at a site distant from the tumor. Various types of vaccines have been proposed, including isolated tumor-antigen vaccines and anti-idiotype vaccines. Another approach is to use tumor cells from the subject to be treated, or a derivative of such cells (reviewed by Schirrmacher et al. (1995) J. Cancer Res. Clin. Oncol. 121:487). In U.S. Pat. No. 5,484,596, Hanna Jr. et al. claim a method for treating a resectable carcinoma to prevent recurrence or metastases, comprising surgically removing the tumor, dispersing the cells with collagenase, irradiating the cells, and vaccinating the patient with at least three consecutive doses of about 107 cells.
International patent application WO 98/04282 (Hiserodt et al.) describes cancer immunotherapy using autologous tumor cells combined with allogeneic cytokine-secreting cells. The vaccines comprise a source of tumor-associated antigen, particularly tumor cells from the patient to be treated, combined with an allogeneic cytokine-secreting cell line. Exemplary cytokines are IL-4, GM-CSF, IL-2, TNF-α, and M-CSF in the secreted or membrane-bound form. The cytokine-producing cells provide immunostimulation in trans to generate a specific immune response against the tumor antigen. Vaccines can be tailored for each type of cancer or for each subject by mixing tumor antigen with an appropriate number of cytokine-producing cells, or with a cocktail of such cells producing a plurality of cytokines at a favorable ratio.
Yet another proposed strategy for immunotherapy is intra-tumor administration of immune effector cells—such as cytotoxic T lymphocytes that are specific for tumor cell antigens or alloantigens. The proximity of the effector cells to the target is supposed to promote the ability of the administered cells to react with the tumor, generating a graft versus tumor response.
Kruse et al. (Proc. Natl. Acad Sci. USA, 87:9377–9381, 1990) analyzed various effector cell populations in adoptive immunotherapy of the 9 L rat gliosarcoma cell line. Different cell populations were prepared that were designed to have a direct effector function against the cancer cells. Included were syngeneic lymphocytes, nonadherent lymphocyte-activated killer (LAK) cells, adherent LAK cells, syngeneic cytotoxic T lymphocytes (CTL) raised against tumor antigens, and allogeneic CTL raised against alloantigens. The allogeneic cytotoxic T lymphocytes were claimed to prevent tumor take. The CTL were prepared by coculturing thoracic duct lymphocytes from one inbred rat strain with spleen cells from rats syngeneic to the challenged animals, under conditions and for a period designed to enrich for cytotoxic effector cells. Treatment was effected by coinjecting the CTL with the tumor cells into the brains of rats in conjunction with recombinant IL-2, and then readministering the CTL on two subsequent occasions. The regimen was claimed to forestall tumor take by 17 days. The authors state that the tumor is successful in the brain, because the brain is an immunologically privileged site which prevents the administered cells from being eliminated before they perform their function. A corollary of this is that the treatment would not be effective at other sites (such as the pancreas and the breast) that are not immunologically privileged.
In a subsequent study, Kruse et al. (J. Neuro-Oncol. 19:161–168, 1994) performed intracranial administrations of single or multiple source allogeneic cytotoxic T lymphocytes. In this study, the 9 L cancer cell line was injected into rats only 6 days before the initiation of treatment. A series of four injections of allogeneic T lymphocytes within the next 17 days was per formed, and had the effect of extending the median life span of the rats by 19 days (about the same interval as the treatment protocol). There is no evidence for any lasting effect, despite the fact that four doses of the effector cells are given. This is consistent with the author's hypothesis that the tumoricidal effect is generated by the CTL themselves, and disappears once the administered cells are eliminated.
Two other publications by the same group demonstrates the natural progression of this CTL implantation technology in a direction towards greater enrichment for cells with a direct effector action against the tumor.
J. M. Redd, et al. Cancer Immunol. Immunother., 34:349, 1992 describe a method of generating allogeneic tumor-specific cytotoxic T lymphocytes. CTL were generated in culture from an inbred rat strain allogeneic to the tumor cell line, and selected and enriched as being specific for a determinant expressed only by the tumor. The ultimate goal of the study is to develop CTL lacking specificity for normal brain antigens. Thus, amongst the CTL populations described earlier in Kruse et al. (Proc. Natl. Acad. Sci,, supra) tumor specific CTL are preferred over allospecific CTL for use in human therapy.
More recently, Kruse et al. (Proc. Am. Assoc. Cancer Res. 36:474, 1995; FASEB J. 10:A1413, 1996) briefly outline a clinical study of human brain cancer patients. The patient's lymphocytes were expanded using OKT3 and IL-2, then co-cultured with allogeneic donor cells for 18–21 days in the presence of IL-2. Such culture conditions would result in a population highly enriched for terminally differentiated CTL effector cells. Patients enrolled in the Phase I study received CTL into the tumor bed, and were placed with a catheter for subsequent infusions. Ongoing treatment involved 1 to 5 treatment cycles every other month, with each cycle consisting of 2–3 CTL infusates within a 1 to 2 week period. Again, the ongoing necessity to readminister the cells is consistent with the author's stated objective of providing cells with a direct cytolytic effect on the tumor.
The necessity of ongoing repeated administration of the effector cells to the tumor through a cannula severely curtails the practical utility of this technology, both in terms of expense and the inconvenience to the patient.
In view of the limitations of previously available strategies, new approaches to the treatment of cancer are needed.
Considerable progress was made towards a simpler and more effective immunotherapeutic strategy by the development of alloactivated cell implants. See International Application WO 96/29394, a “Method for Treating Tumors” (G. A. Granger). Stimulated cellular compositions are placed directly into the tumor bed, leading to beneficial effects for patients with different types of cancers. The method can be conducted by coculturing lymphocytes derived from a healthy allogeneic donor with leukocyte stimulator cells obtained from the patient. The alloactivated donor cells are then surgically implanted at the tumor site, resulting in a response against the tumor. Without intending any limitation on the therapeutic composition or method, it is believed that the implanted cells produce a mixture of cytokines which recruit host cells. The recruited host cells then identify both the implanted lymphoid cells and tumor tissue as foreign.